This invention relates generally to a machine for digging holes in the ground.
Poles for power lines and communication purposes, for example, are required to be vertical and arranged in straight lines. The poles may be planted in positions which are relatively inaccessible. It follows that the point at which holes for the poles are made and the directions of the holes may call for precision work and this in turn may demand significant outreach of a crane which is used in making the holes.
One type of hole digger which is known to the applicant as a digger derrick consists of a telescopic mobile crane from which is suspended a torque head. An auger or other type of hole making device which is able to handle the conditions of the ground in which the hole is to be made, is suspended from the crane.
Advantages of the digger derrick include the ability of the crane to be extended to the required extent and then to be positioned so that the hole making device is accurately located at the site of the required hole.
The hole making device may be mounted on a separately slidable saddle so that it can, at an operator's choice, be stowed in a fixed position which enables the crane to be used for conventional lifting purposes, or to be unstowed and attached to a telescoping portion of the crane so that it can be brought precisely to the required site for the hole, which may be some distance from a vehicle which carries the crane.
It is apparent therefore that by extending the crane the hole digging device can be positioned at a location which is not accessible to the vehicle and by adjusting the position of the crane it is not necessary for the vehicle to be parked at a precise distance or orientation relatively to the hole site.
Depending on the nature of the digging device, its digging element may be fed into the ground by downwards motion of the crane. An alternative method which is particularly associated with the drilling of hard rock, involves a feed element which includes a feed track. The crane is used only to place and hold the feed track in position. Drilling is done by rotating a drill head and feeding it down the track using a suitable feed mechanism. This approach eliminates misalignment effects which could be caused by radial movement of the crane, in the digger derrick, and makes it possible to apply greater force to the digging element.
The generation of the required rotary and feed motions for the digging element and the feed element call, in turn, for the provision of a number of services at the end of a boom from which the devices are supported, such as hydraulic oil and compressed air lines. The services however have to cope with the telescopic motion of the boom which occurs when the digging element is readied for work and subsequently is stowed and this requirement can give rise to problems.